During the drilling of an oil and gas well, long strings of pipe are strung together to form a drill string or to form a casing string to line the well bore. These pipe strings are usually supported by rotary spiders that fit into or over the opening of a rotary table on the drilling rig. Spiders typically employ slips that are peripherally distributed around an inwardly tapered cylindrical bowl. The slips are typically fitted with detachable gripping dies. Such gripping dies having a plurality of teeth the form a pipe gripping surface to increase the grip of the slips on the pipe string.
Spider slips are typically attached to a slip timing ring by a linkage so that upward and downward movement of the slip timing ring will simultaneously move the slips upward and downward in the slip bowl for engaging and releasing the pipe string. Vertically extending hydraulically or pneumatically powered cylinders having extendable and retractable pistons and rods are typically used to raise and lower the slip timing ring.
When a pipe string suspended in the well is to be gripped by the spider, the piston rods of the hydraulic cylinders are retracted to move the timing ring and thus the slips downward so that the inwardly tapered slip bowl surface will urge the downwardly moving slips radially inward to bear upon and grip the pipe. When the pipe string is to be released, the piston rods of the hydraulic cylinders are extended to move the timing ring and thus the slips upward in the tapered slip bowl so that the upwardly moving slips move radially outward away from the pipe string in order to release the pipe.
Ideally, the spider is designed to have the lowest possible elevation profile with respect to the top of the rotary table. Lowering the elevation profile of the spider above the top of the rotary table will provide workers with more work room and offer less interference in the work space area around the spider. Flush mounted spiders having the slip bowl and slip assemblies and the hydraulic cylinders used to power the slips upward and downward all within the confines of the rotary table opening. Such flush mounted spiders often have a lower elevation profile above the top of the rotary table.
In drilling rigs with small rotary table openings particularly 17½ inch or less, there is often insufficient room within the rotary table opening for a flush mounted spider that utilizes a power slip mechanism such as hydraulic cylinders to raise and lower the slips. In situations where such a spider will fit in the rotary table opening, its pipe size and pipe weight capacity is often severely limited. Such limitations on the pipe size and pipe weight capacity may present safety concerns as well as limitations on the depth and type of well in which the spider is to be utilized. In such situations powered spiders that rest upon the top of the rotary table are utilized. However, the slip bowl and the hydraulic cylinders of these top mounted spiders will often extend the elevation profile of the spiders several feet above the top of the rotary table.
Consequently, there is a need for a rotary table spider that will have or approach the low elevation profile of many flush mounted spider designs. Further, there is a need for a powered rotary table spider that may be utilized on rotary table having a small opening but that will still offer a high torque and weight capacity.